To build a system with a minimum cost, some fraction of the storage should be low cost (and perhaps low efficiency) and some should be high efficiency and higher cost. Lowest cost will come with some amount of excess generation, enough short term storage to cover daily to a week or so, and some lower efficiency longer term storage.

This is the point to something like hydrogen fuel cells, which is a type of flow battery. Flow batteries are generally not potentially useful for cars, as the potential low cost technologies have low specific energy densities (kWh/mass).

WetEV#49Most everything around here is wet during the rainy season. And the rainy season is long.2012 Leaf SL Red (Totaled)2014 Leaf SL Red

RegGuheert wrote:... and can achieve a 70% round-trip efficiency[/url]. That's the kind of performance we need to achieve to make long-term storage a viable possibility.

I disagree.

Long term storage is more driven by cost than efficiency. The opposite of short term storage.

Actually, both long-term and short-term storage are driven by cost. (That's why there is virtually no installed storage beyond pumped hydro.) They have different cost drivers, but efficiency is a key driver for both of them.

WetEV wrote:Let me try out an example to illustrate:

$0.10 primary generation from solar cells. 10% ROI + expenses.

Your example fails here. You assumed that the per-kWh cost of generation is the same for every bit of generation which is added. In fact, the per-kWh cost of generation goes up as more is added, since additional generation results in lower-and-lower additional kWh of generation. In the extreme case, once you have enough generation, additional generation has an infinite per-kWh cost since it provides no additional generation. (It may have other value, however, such as redundancy or margin.)

But we CAN readily calculate the relative costs of the low- and high-efficiency long-term storage options since the author of the article I linked provided details of how those two options impact the overall performance of the system. Here are the numbers:

So this result agrees with your conclusion in that the lower-efficiency solution is cheaper. But the ONLY reason for that is that the natural gas generators already exist as does some of the natural gas storage. I used TODAY'S costs for solid oxide fuel cells. If in 2030, the solid-oxide fuel cells are the same cost or cheaper than natural gas turbines, then the result goes the other way by a long shot for systems that do not already have the gas turbines.

Let's see what the author comes up with regarding the 2030 cost model for these scenarios.

Anyway, the author did not price the fuel-cell option. Here is what he came up with for system costs using natural gas generators:

The bottom line is that he projects wholesale costs to be between 6.1 c/kWh and 9.2 c/kWh in by the year 2030. If his numbers are in the ballpark, it seems possible that Texas could pull this off. They certainly have a much better chance than Germany of being able to do this.